feat(v4.0.0): vocabularies, to FORTH-79

- VOCABULARY DEFINITIONS CONTEXT CURRENT FORTH, and v3's ORDER.  A name is
  looked up in the CONTEXT vocabulary and then in FORTH; a new entry goes
  into the CURRENT vocabulary; : makes the CURRENT vocabulary CONTEXT;
  FORTH is immediate.
- WORDS lists the CONTEXT vocabulary.  FORGET takes what was defined later
  out of every vocabulary, and a vocabulary that goes gives way to FORTH.
- v3's vocabularies separate nothing: a word defined in one is found from
  every other, and one redefined in a vocabulary replaces FORTH's for good.
- tests/test_host_quit.c: isolation, chaining to FORTH, two vocabularies
  with the same names, FORGET across them; and DUMP is now checked to put
  BASE back.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/capsule/dict.v4

@@ -26,7 +26,15 @@
 \
 \ Constants the loader supplies:
 \   DP        word address of the variable: the next free byte
-\   (LATEST)  word address of the variable: the xt of the newest entry, or 0
+\   (LATEST)  word address of the variable: the xt of the newest entry of the
+\             FORTH vocabulary, or 0
+\   CONTEXT CURRENT   word addresses of the variables: each holds the address
+\             of a vocabulary's head cell -- the cell that holds the xt of
+\             that vocabulary's newest entry.  FORTH's head cell is (LATEST).
+\
+\ VOCABULARIES (FORTH-79).  A name is looked up in the CONTEXT vocabulary and
+\ then, if that is not FORTH, in FORTH.  A new entry goes into the CURRENT
+\ vocabulary: it is linked to that vocabulary's newest entry and becomes it.
 \   DBASE DLIMIT   byte addresses of the start and end of dictionary space
 \   PAD       byte address of the scratch area for strings, 84 bytes or more
 \   (D)       word address of five cells of scratch for this file
@@ -78,7 +86,7 @@ header 2,
 : 2, ( lo hi -- )      SWAP , , ;                       \ the low cell first, as v3
 
 header LATEST
-: LATEST ( -- xt )     (LATEST) a! @ ;
+: LATEST ( -- xt )     CURRENT a! @ a! @ ;         \ the newest entry of the CURRENT vocabulary
 
 \ ---- the fields of an entry (5.13) -----------------------------------------
 
@@ -118,7 +126,7 @@ header HIDDEN
 \ ---- making an entry -------------------------------------------------------
 \ (D)+0 where the name starts   (D)+1 the name being looked up
 \ (D)+2 the name being copied, or the entry being looked at
-\ (D)+3 a count
+\ (D)+3 a count                 (D)+4 whether a lookup has gone on to FORTH
 
 \ ( -- bytes )   what an entry for a name of (D)+3 characters takes: its name
 \ cells and three more
@@ -146,7 +154,7 @@ header HIDDEN
   P: DP b! @b 3 and if ALIGNED  drop 0 C,  jump P
   ALIGNED: drop
   0 ,  (D) a! @ ,  LATEST ,
-  HERE (LATEST) a! ! ;
+  HERE CURRENT a! @ a! ! ;
   FULL: drop ;                               \ (DP+) has set NODE-ERROR
   EMPTY: drop  NODE-ERROR b! 6 !b ;             \ name missing
 
@@ -162,7 +170,8 @@ header HIDDEN
   C@ -32 + -if LONG  drop jump CUT
   LONG: drop  31 (D)+1 a! @ C!
   CUT:
-  LATEST
+  0 (D)+4 a! !                               \ not yet on to FORTH
+  CONTEXT a! @ a! @
   L: if END
      (D)+2 a! !
      (D)+2 a! @ -3 + a! @ 2 and if VISIBLE  drop jump OLDER
@@ -176,7 +185,11 @@ header HIDDEN
         EQ: drop jump C
      SAME: drop  (D)+2 a! @ ;
      OLDER: (D)+2 a! @ -1 + a! @  jump L
-  END: ;
+  END: (D)+4 a! @ if FIRST  drop ;           \ FORTH has been searched: not found
+  FIRST: drop  -1 (D)+4 a! !
+     CONTEXT a! @ (LATEST) xor if ISFORTH    \ CONTEXT is FORTH: that was it
+     drop drop  (LATEST) a! @  jump L
+  ISFORTH: drop ;
 
 \ ( -- xt | 0 )   FORTH-79: the compilation address of the next word in the
 \ input stream, or 0 if it is not in the dictionary.